Metal-Organic Frameworks (MOFs) are of interest for gas separations and catalysis. In some cases, when guests become bound to MOFs the structure and electronic characteristics of the MOF change significantly. MOFs with open-metal sites such as Fe2(dobdc) (where dobdc4-=2,5-dioxodo-1,4-benzenedicarboxylate) are particularly susceptible to such changes because of the direct metal-adsorbate bonding interactions enabled by the unique metal coordination environment. When C2H6 and N2O reacted in the presence of Fe2(dobdc), N2 and C2H5OH were made. This reaction went through an iron-oxo intermediate [Fe2(O)2(dobdc)] and Fe2(OH)2(dobdc) was isolated as the stable product. The elucidation of the electronic structure differences between Fe2(dobdc), Fe2(OH)2(dobdc), and Fe2(O)2(dobdc) may help to understand how MOFs could be altered to favor magnetic or reactive characteristics that have useful applications. Periodic Density Functional Theory (DFT) can contribute to the understanding of the electronic characteristics of these materials. In this study, the isotropic couplings within Fe2(dobdc), Fe2(OH)2(dobdc), and Fe2(O)2(dobdc) were computed with PBE+U, HSE, and HSE+D using VASP. Density of states calculations were performed with PBE+U and HSE to compare the band gaps of each structure. The Bulk moduli for all structures were computed to find the optimal unit cell volumes. Preliminary findings indicate that Fe2(dobdc) has weak ferromagnetic couplings between the quintet Fe(II) ions within each iron channel and weak antiferromagnetic coupling between the iron channels. Stronger intrachannel antiferromagnetic couplings are present between the quintet Fe(IV) ions within the Fe2(O)2(dobdc) intermediate species and much stronger antiferromagnetic inter and intrachannel couplings between the sextet Fe(III) ions was observed in the case of Fe2(OH)2(dobdc). These calculations indicate that Fe2(dobdc) has a unique structure that results in unusual high spin Fe(IV)-oxo groups that provide a unique catalytic environment for C2H6.

Periodic DFT analysis of Fe-MOF-74 and new structures derived from activation with N<sub>2</sub>O

247th National Meeting (2014)

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Periodic DFT analysis of Fe-MOF-74 and new structures derived from activation with N2O

Periodic DFT analysis of Fe-MOF-74 and new structures derived from activation with N₂O